Rule - MD039

Property	Value
Aliases	md039, no-space-in-links
Autofix Available	Yes
Enabled By Default	Yes

Summary

Do not include spaces inside link text labels.

Reasoning

Readability

Link labels with leading or trailing spaces (e.g., [ label ]) are visually indistinct from those without (e.g., [label]). Enforcing consistent spacing prevents accidental mismatches in link reference resolution and improves source readability.

Examples

Failure Scenarios

This rule triggers when the link label for any link or image includes leading whitespace or trailing whitespace.

this is not
[ a proper](https://www.example.com)
link

Explanation: The link label a proper has a leading space. The rule requires that link labels do not have a space at the very beginning or the very end of the label, while spaces between words remain allowed.

Unlike the previous example which had leading whitespace, this case demonstrates trailing whitespace inside the link label.

this is not
[label ](https://www.example.com)
link

Explanation: The link label label has a trailing space. The rule requires that link labels do not have a space at the very beginning or the very end of the label, while spaces between words remain allowed.

Unlike the previous examples which had only leading or only trailing whitespace, this case demonstrates both leading and trailing whitespace inside the link label.

this is not
[ label ](https://www.example.com)
link

Explanation: The link label label has both a leading space and a trailing space. The rule requires that link labels do not have a space at the very beginning or the very end of the label, while spaces between words remain allowed.

Unlike the previous examples which used standard links, this case demonstrates leading whitespace in an image's alt-text label.

![ alt text](https://www.example.com/image.png)

Explanation: The image alt-text label alt text has a leading space. The rule applies to both links and images, and neither may have a space at the very beginning or the very end of the label, while spaces between words remain allowed.

Unlike the previous examples which used inline links or images, this case demonstrates leading and trailing whitespace in a link reference definition label.

[ label ]: https://www.example.com

Explanation: The link reference definition label label has both a leading space and a trailing space. The rule applies to link reference definitions as well, and neither may have a space at the very beginning or the very end of the label, while spaces between words remain allowed.

Correct Scenarios

This rule does not trigger when the link label for any link or image does not start with leading whitespace or end with trailing whitespace.

this is a
[proper](https://www.example.com)
link

Explanation: The link label proper does not contain any leading or trailing whitespace. It adheres to the rule's requirement for clean link labels.

Unlike the previous example which used a single-word label, this case demonstrates a multi-word label with an internal space, which is permitted as long as there are no leading or trailing spaces.

this is
[a proper](https://www.example.com)
link

Explanation: The link label a proper does not contain any leading or trailing whitespace. It adheres to the rule's requirement for clean link labels. Internal spaces within the label are allowed.

Unlike the previous example which used a standard link, this case demonstrates an image with a clean alt-text label without leading or trailing whitespace.

![alt text](https://www.example.com/image.png)

Explanation: The image alt-text label alt text does not contain any leading or trailing whitespace. It adheres to the rule's requirement for clean labels in both links and images.

Unlike the previous examples which used inline links or images, this case demonstrates a link reference definition label without leading or trailing whitespace.

[label]: https://www.example.com

Explanation: The link reference definition label label does not contain any leading or trailing whitespace. It adheres to the rule's requirement for clean labels in link reference definitions.

Fix Description

The fix for this rule strips leading and trailing spaces from the link label.

Configuration

Prefixes
plugins.md039.
plugins.no-space-in-links.

Value Name	Type	Default	Description
enabled	boolean	True	Whether the Rule Plugin is enabled.

Origination of Rule

This rule is largely inspired by the MarkdownLint rule MD039.

Differences From MarkdownLint Rule

The difference between this rule and the original rule is that the original rule only fired on links, not image links or link definitions. As the only difference between a link:

[a link](https://www.example.com)

and an image:

![an image](https://www.example.com)

is the ! character, it made sense for the implementation to respect both elements.